The present invention relates to a semiconductor laser apparatus, semiconductor laser module, optical transmitter and wavelength division multiplexing communication system, all of which are used in the optical communication system.
In recent years, various new techniques have been developed in the field of semiconductor laser used in the optical communication system. For example, in the wavelength division multiplexing (WDM) communication system, a single-mode laser (e.g., distributed feedback (DFB) laser) has usually been used as a source of signal light. In a dense WDM system (DWDM system), however, a crosstalk between channels may occur to deteriorate signals when the lasing wavelength of the signal light source is out of a predetermined level. To avoid such a problem, a technique of regulating the wavelength of the laser beam launched from a light-emitting device has been developed.
For example, there has been proposed a semiconductor laser apparatus which comprises a light-emitting device for outputting a laser beam and a wavelength monitoring portion for sensing the wavelength of the laser beam outputted from the light-emitting device and which can control the light-emitting device relating to its temperature based on the wavelength of the laser beam sensed by the wavelength monitoring portion so as to control the wavelength of the laser beam launched from the light-emitting device.
A semiconductor laser apparatus of the present invention comprises a light-emitting portion including a light-emitting device for outputting a laser beam, a light-receiving element for receiving the laser beam outputted from said light-emitting device, a wavelength monitoring portion including an optical system disposed between said light-emitting device and said light-receiving element, a control portion for controlling the wavelength of the laser beam outputted from said light-emitting device by controlling the temperature of said light-emitting device based on the wavelength of the laser beam detected by said wavelength monitoring portion, an optical isolator disposed on the optical path between said light-emitting device and said wavelength monitoring portion for preventing the light from returning from said wavelength monitoring portion back to said light-emitting device, and a temperature regulating portion for independently controlling the temperatures of said light-emitting portion and wavelength monitoring portion.
A semiconductor laser module of the present invention comprises a semiconductor laser apparatus having a light-emitting portion including a light-emitting device for outputting a laser beam, a light-receiving element for receiving the laser beam outputted from said light-emitting device, a wavelength monitoring portion including an optical system disposed between said light-emitting device and said light-receiving element, a control portion for controlling the wavelength of the laser beam outputted from said light-emitting device by controlling the temperature of said light-emitting device based on the wavelength of the laser beam detected by said wavelength monitoring portion, an optical isolator disposed on the optical path between said light-emitting device and said wavelength monitoring portion for preventing the light from returning from said wavelength monitoring portion back to said light-emitting device and a temperature regulating portion for independently controlling the temperatures of said light-emitting portion and wavelength monitoring portion, a package being configured to seal at least the light-emitting portion in said semiconductor laser apparatus in an air-tight manner, and an optical fiber being configured to receive and externally transmitting the laser beam outputted from said semiconductor laser apparatus.
The present invention provides an optical transmitter for transmitting optical signals in a wavelength division multiplexing communication system, comprising a semiconductor laser module having a light-emitting device for outputting a laser beam, a light-receiving element for receiving the laser beam outputted from said light-emitting device, a wavelength monitoring portion including an optical system disposed between said light-emitting device and said light-receiving element, a control portion for controlling the wavelength of the laser beam outputted from said light-emitting device by controlling the temperature of said light-emitting device based on the wavelength of the laser beam detected by said wavelength monitoring portion, an optical isolator disposed on the optical path between said light-emitting device and said wavelength monitoring portion for preventing the light from returning from said wavelength monitoring portion back to said light-emitting device, and a temperature regulating portion for independently controlling the temperatures of said light-emitting portion and wavelength monitoring portion.
The present invention also provides a wavelength division multiplexing communication system having a plurality of optical transmitters for transmitting optical signals, a multiplexer for wavelength multiplexing multi-channel optical signals transmitted from said optical transmitters, a plurality of optical amplifiers connected to one another in a plurality of stages for amplifying and relaying the multiplexed optical signal from said multiplexer, a branching filter for wavelength separating the amplified optical signals from the optical amplifiers for the respective channels and a plurality of optical receivers for receiving the respective optical signals separated by the branching filter, each of said optical transmitters comprising a semiconductor laser module having a light-emitting portion including a light-emitting device for outputting a laser beam, a light-receiving element for receiving the laser beam outputted from said light-emitting device, a wavelength monitoring portion including an optical system disposed between said light-emitting device and said light-receiving element, a control portion for controlling the wavelength of the laser beam outputted from said light-emitting device by controlling the temperature of said light-emitting device based on the wavelength of the laser beam detected by said wavelength monitoring portion, an optical isolator disposed on the optical path between said light-emitting device and said wavelength monitoring portion for preventing the light from returning from said wavelength monitoring portion back to said light-emitting device, and a temperature regulating portion for independently controlling the temperatures of said light-emitting portion and wavelength monitoring portion.